Vaccination using defined antigens has been unsuccessful in leishmaniasis due to an inadequate understanding of the immune events leading to disease. We are pursuing recent findings in the mouse model of leishmaniasis to investigate the cellular response to infection in humans, both in vitro and in vivo. A clinical protocol is in place in Varanasi, India, to study human bone marrow and splenic aspirates obtained during routine clinical evaluation of patients with visceral leishmaniasis. RNA is prepared and semi-quantitated using RT-PCR to determine the cytokine transcripts in patients with active and cured disease. Grants from the Vaccine Action Programme and the WHO/TDR fund travel for the US investigators and travel, equipment, supplies, and personnel for the Indian site. The group in Vit-ria, Brazil is looking at the potential for genetic factors to influence the immune response to infection. We are evaluating polymorphisms in cytokine gene promoter regions in families with kala-azar. We will continue to develop both the Indian and Brazilian sites as potential places for clinical vaccine trials. In the CBER laboratory, we are investigating the in vitro response to infection with promastigotes and amastigotes by evaluating the IFNg receptor activation pathway in macrophages and macrophage-like cells.